A "Scalp Cookie" is a small patch of dry scalp anywhere on the head, (sometimes brought on by hair products) that often compells a person to scratch or pick at the area of dry skin for long periods of time. This is also a nervous habit for some. There is ususally a pleasurable feeling or release associated with the scratching or subtle picking of the scalp cookie in question.

I'm digging for scalp cookies or "ooh I just found a good scalp cookie to pick out